In situ flue gas analyzer with improved process communication

ABSTRACT

An in situ flue gas analyzer includes a probe extendable into a flue. The probe has a measurement cell providing a signal responsive to a concentration of a gas within the flue. A controller is coupled to the probe and configured to provide an output based on the signal from the measurement cell. A first media access unit is coupled to the controller and is operably coupleable to a first process communication link. The first media access unit is configured to communicate in accordance with an all-digital process communication protocol. A second media access unit is coupled to the controller and is operably coupleable to a second process communication link. The second media access unit is configured to communicate in accordance with a second process communication protocol that is different than the all-digital process communication protocol. The first and second media access units are enabled simultaneously.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on and claims the benefit of U.S.Provisional Patent Application Ser. No. 61/806,621, filed Mar. 29, 2013,the content of which is hereby incorporated in its entirety.

BACKGROUND

Industrial process industries often rely on energy sources that includeone or more combustion processes. Such combustion processes includeoperation of a furnace or boiler to generate energy from combustion,which is then used for the process. While combustion provides relativelylow-cost energy, its use is typically regulated and combustionefficiency is sought to be maximized. Accordingly, one goal of theprocess management industry is to reduce the production of greenhousegases by maintaining combustion efficiency of existing furnaces andboilers.

In situ or in-process flue gas analyzers are commonly used formonitoring, optimizing and/or controlling combustion processes.Typically, these analyzers employ an oxygen sensor that is similar inboth technology and application to oxygen sensors found in automobiles.Such sensors are heated to an elevated temperature and provide a sensoroutput that is indicative of a parameter of interest (oxygen) relativeto the exhaust/flue gas stream. In situ or in-process analyzers areparticularly advantageous because they have no moving parts or samplingapparatus resulting in an extremely reliable probe that requires verylittle maintenance. While in situ flue gas analyzers may be consideredto be field devices in the sense that they are often located out in thefield and subjected to climatological extremes of temperature, humidity,mechanical vibration, and electrical interference, they aresubstantially different from most field devices. While many fielddevices measure a single physical quantity, such as temperature,pressure or flow, of a process fluid, process analyzers actually measurethe composition of flue gas process streams. Accordingly, the processingperformed within a flue gas analyzer is relatively complex andhigh-speed. Thus, the flue gas analyzer must often perform significantcalculations and analyses in order to effectively control a combustionprocess. Additionally, it must do so quickly since the flue gasconcentration sensor signal can also vary quickly.

Traditionally, some in situ flue gas analyzers were provided thatcommunicated in accordance with a hybrid digital-analog processcommunication protocol. An example of this process communicationprotocol is the digital Highway Addressable Remote Transducer (HART®)protocol. The HART® communication protocol specifies the manner in whichdigital information is arranged in digital packets (i.e., HART® packets)and the manner in which the digital packets are physically conveyedthrough the wired transmission media. Typically, an in situ flue gasoxygen transmitter, such as that sold under the trade designation Model6888 Oxygen Transmitter from the Rosemount Analytical, Inc. businessunit of Emerson Process Management, transmits its flue gas concentrationinformation in accordance with an analog signaling technique, such asthe well-known 4-20 milliamp signaling technique. Optionally, thetransmitter can be configured or otherwise specified to provide ananalog signal representing flue gas oxygen in the form of a rawmillivolt signal in order to interoperate with a variety of systems.Additionally, since the HART® protocol superimposes digital informationupon the analog process variable signal, it is also known for an in situflue gas oxygen transmitter to transmit digital information to anoptional user interface, such as the known Xi Electronics moduleavailable from Rosemount Analytical.

While existing products provide significant benefits for users thereofin the monitoring and/or controlling of combustion processes, the sheervolume of data generated by the analysis of the flue gas stream and thespeed with which the constituents of the flue gas stream may change, canbe a challenge for the communications of the flue gas analyzer.Providing an in situ flue analyzer with improved process communicationabilities would benefit the art of process combustion monitoring andcontrol.

SUMMARY

An in situ flue gas analyzer includes a probe extendable into a flue.The probe has a measurement cell providing a signal responsive to aconcentration of a gas within the flue. A controller is coupled to theprobe and is configured to provide an output based on the signal fromthe measurement cell. A first media access unit is coupled to thecontroller and is operably coupleable to a first process communicationlink. The first media access unit is configured to communicate inaccordance with an all-digital process communication protocol. A secondmedia access unit is coupled to the controller and is operablycoupleable to a second process communication link. The second mediaaccess unit is configured to communicate in accordance with a secondprocess communication protocol that is different than the all-digitalprocess communication protocol. The first and second media access unitsare enabled simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of an in situ flue gas analyzer with whichembodiments of the present invention are particularly useful.

FIG. 2 is a diagrammatic perspective view of an in situ flue gasanalyzer in accordance with an embodiment of the present invention.

FIG. 3 is a block diagram of an in situ flue gas analyzer in accordancewith an embodiment of the present invention.

FIG. 4 is a diagrammatic view of an in situ flue gas analyzer operatingwithin a combustion process in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 is a diagrammatic view of an in situ flue gas analyzer operatingin a combustion process. One example of such an analyzer 10 is that soldunder the trade designation Model 6888 In Situ Flue Gas OxygenTransmitter available from Rosemount Analytical Inc. Analyzer 10includes a probe assembly 12 that is disposed within a stack or flue 14and measures at least one parameter related to combustion occurring atburner 16. Typically, analyzer 10 is an oxygen analyzer, but can be anydevice that measures any suitable parameter related to constituentswithin the flue gas stream.

Burner 16 is operably coupled to a source of air or oxygen 18 and asource 20 of combustible fuel. Each of sources 18 and 20 is preferablycoupled to burner 16 through a respective valve to deliver a controlledamount of oxygen and/or fuel to burner 16 in order to control thecombustion process. Analyzer 10 measures the amount of oxygen in thecombustion exhaust flow and provides an indication of the oxygen levelto combustion controller 22. In the past, this signal was an analogsignal either in the form of a 4-20 milliamp current loop or a rawmillivolt signal. Controller 22 controls one or both of valves 24, 26 toprovide closed loop combustion control. Analyzer 10 includes an oxygensensor that typically employs a zirconia oxide sensor substrate toprovide an electrical signal indicative of oxygen concentration, contentor percentage in the exhaust. Zirconia oxide sensors operate at atemperature of about 700° Celsius and thus analyzer 10 includes, withinprobe assembly 12, an electrical heater that is operably coupled to ACpower source 29. The oxygen sensor within probe 12 is similar intechnology to oxygen sensors found in automobiles. Such sensors arehighly effective in permitting control systems to maintain optimum fuelto ratios in order to achieve high efficiency, low NO_(x) production,and also the least amount of greenhouse gas emissions possible.

FIG. 2 is a diagrammatic perspective view of an in situ flue gasanalyzer in accordance with an embodiment of the present invention.Probe assembly 12 is generally configured to house a sensor coreassembly which includes diffuser disposed proximate end 32. Themeasurement cell within probe 12 is operable at an elevated temperatureand the elevated temperature. The measurement cell and heater withinprobe 12 are electrically coupled to analyzer electronics (shown in FIG.3) within electronics housing 36. Analyzer electronics 42 is configuredto obtain a measurement from the measurement cell and provides suitablesignal conditioning in order to provide a signal representing flue gasoxygen. Additionally, analyzer electronics 42 includes a controller orother suitable circuitry to control energization of the heater withinprobe 12 in order to maintain suitable thermal control of themeasurement cell.

In accordance with an embodiment of the present invention, analyzerelectronics 42 also includes a plurality of media access units tocommunicate in accordance with a plurality of distinct processcommunication protocols, such as the HART® process communicationprotocol described above and the FOUNDATION™ Fieldbus (FF). Inaccordance with an embodiment of the present invention, analyzerelectronics 42 communicates using a plurality of distinct processcommunication protocols simultaneously or at substantially the sametime. Thus, communication in accordance with a first processcommunication protocol may be performed for a first purpose, such ascombustion burner control, and communication in accordance with thesecond distinct process communication protocol may be done in order toprovide a second purpose, such as interacting with an optional userinterface, such as the Model Xi operator interface (shown in FIG. 4)available from Rosemount Analytical Inc.

FIG. 3 is a block diagram of an electronics board of an in situ flue gasanalyzer in accordance with an embodiment of the present invention.Electronics 42 includes power module 50 that is configured to receive ACelectrical power, such as 110 or 220 VAC and condition the power forprovision to various components of the analyzer. Additionally, since theheater within probe 12 will typically receive the full AC voltage, powermodule 50 will also generally include at least one line that passes toswitch 53 such that full AC voltage to the heater can be controlled bycontroller 52. Controller 52 is coupled to first and second media accessunits (MAU) 54 and 56, respectively. Each media access unit 54, 56 isoperably coupleable to communication media appropriate for thatrespective media access unit. While terminals 58, 60, 62, and 64 areshown, it is noted that if either of media access units 54, 56 is awireless media access unit, the terminals for that respective mediaaccess unit may simply be replaced with a coupling to an antenna.Additionally, while four distinct terminals 58, 60, 62 and 64 are shown,it is also contemplated that the common or ground of the circuit may beshared, such that only three terminals need be actually provided. In oneembodiment, media access unit 54 is configured to communicate inaccordance with the known HART® process communication protocol. In suchembodiment, terminals 58 and 60 may be operably coupled to a userinterface, such as the Xi Operator Interface available from RosemountAnalytical Inc., or any other suitable device that can receive andprovide a useful function relative to the HART® communication. Mediaaccess unit 56 is configured to communicate in accordance with anall-digital process communication protocol. All-digital processcommunication protocols are generally considered to be somewhat fasterthan hybrid-based process communication protocols. An example of anall-digital process communication protocol includes the FF processcommunication protocol as well as the known PROFIBUS-PA processcommunication protocol. The FF protocol is an all-digital, serial,two-way communication protocol that provides a standardized physicalinterface to a 2 or 4-wire loop or bus interconnecting field devices,such as sensors, actuators, controllers, valves, et cetera, that may,for example, be located in an instrumentation or process controlenvironment of factory or plant. The FF protocol provides a local areanetwork for field devices within a process to enable these devices tointeroperate and perform control functions at locations distributedthroughout the process and to communicate with one another before andafter performance of these control functions to implement an overallcontrol strategy. The FF protocol generally provides relatively highspeed digital communication, which speed is particularly advantageousfor the communication of flue gas stream constituent information inaccordance with embodiments of the present invention. This is becausesuch analyzers must generally measure the composition of the flue gasprocess streams and provide information indicative of such compositionto a controller of the combustion process or Distributed Control System(DCS). Additionally, since the combustion process occurs quite rapidly,the flue gas stream constituents can vary quickly. Thus, it is quiteadvantageous for media access unit 56, which communicates in accordancewith an all-digital process communication protocol, to be coupled to adistributed control system and/or to combustion controller 22illustrated with respect to FIG. 1.

FIG. 3 also illustrates measurement circuitry 66 being operably coupledto controller 52 as well as terminals 68 and 70. Terminals 68 and 70couple to the measurement cell within probe 12 and thus measurementcircuitry 66 is able to provide a digital indication of the analogmeasurement cell output. Measurement circuitry 66 may include one ormore suitable analog-to-digital converters as well as linearizationcircuitry and/or suitable filters, as appropriate.

FIG. 4 is a diagrammatic view of a process combustion monitoring andcontrol system in accordance with an embodiment of the presentinvention. Many components of the system shown in FIG. 4 are similar tothat shown in FIG. 1 and like components are numbered similarly. FIG. 4shows in situ flue gas analyzer 110 communicating with combustioncontroller 22 via link 100. This communication link 100 between in situflue gas analyzer 110 and combustion controller 22 is all-digitalprocess communication, such as that in accordance with the FF protocol.Additionally, in situ flue gas analyzer 110 is operably coupled to userinterface 28 via a second communication link 102. Link 102 may be inaccordance with a known hybrid process communication protocol, such asthe HART® process communication protocol. This allows embodiments of thepresent invention to function with legacy Xi User Interfaces availablefrom Rosemount Analytical Inc., which are configured to receive HART®data and provide useful user interface functions relative to the gasanalyzer. However, the communication link 100 between in situ flue gasanalyzer 110 and process combustion controller 22 is a high speed,all-digital link. Thus, embodiments of the present invention generallyinclude a first link or channel from in situ flue gas analyzer 110 to acombustion control system having a first data communication rate, and asecond link or channel from the in situ flue gas analyzer 110 to asecond device, such as a user interface thereof, having processcommunication in accordance with a second protocol having a secondcommunication rate, where the first communication rate is higher thanthe second communication rate. Communication on the first and secondlinks occurs simultaneously, or substantially simultaneously. As usedherein, “substantially simultaneously” is intended to mean that althoughphysical layer signaling on both links may not be occurring during thesame instant, such signaling occurs within a short period, such as oneminute. Additionally, the communication on each link occurs with suchfrequency that analyzer 110 is considered to be online with respect toeach link. Accordingly, even when analyzer 110 is not activelytransmitting data on the first and second links, analyzer 110 ismonitoring such links for communication. Thus, it can be said that bothlinks and the corresponding media access units within analyzer 110 areenabled simultaneously. Accordingly, changes in the flue gas constituentconcentrations occurring rapidly within flue 14 can be analyzed andcommunicated very rapidly to combustion analyzer 22 for more effectivecontrol, while information relative to a user interface can be exchangedwith optional user interface 28 at a slower rate. Additionally, theutilization of multiple process communication protocols insures thatuser interface communication does not consume bandwidth on thedistributed control system link 100 or otherwise interfere with DCScommunication. This further increases the effectiveness of theall-digital communication link between process combustion flue gasanalyzer 110 and combustion controller 22.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. An in situ flue gas analyzer comprising: a probeextendable into a flue, the probe having a measurement cell providing asignal responsive to a concentration of a gas within the flue; acontroller coupled to the probe and configured to provide an outputbased on the signal from the measurement cell; a first media access unitcoupled to the controller and operably coupleable to a first processcommunication link, the first media access unit being configured tocommunicate in accordance with an all-digital process communicationprotocol; a second media access unit coupled to the controller andoperably coupleable to a second process communication link, the secondmedia access unit being configured to communicate in accordance with asecond process communication protocol that is different than theall-digital process communication protocol; and wherein the first andsecond media access units are enabled simultaneously
 2. The in situ fluegas analyzer of claim 1, wherein the measurement cell includes an oxygensensor.
 3. The in situ flue gas analyzer of claim 1, wherein theall-digital process communication protocol is in accordance with theFOUNDATION Fieldbus protocol.
 4. The in situ flue gas analyzer of claim1, wherein a communication rate of the all-digital process communicationprotocol is faster than a communication rate of the second processcommunication protocol.
 5. The in situ flue gas analyzer of claim 1,wherein the second process communication protocol is a hybrid processcommunication protocol.
 6. The in situ flue gas analyzer of claim 5,wherein the hybrid process communication protocol superimposes a digitalsignal on an analog signal.
 7. A process combustion control systemcomprising: a combustion source operably coupled to a source of fuel anda source of air, the combustion source being configured to providecombustion gasses through a flue; a combustion controller coupled to atleast one of the source of fuel and source of air; an in situ flue gasanalyzer coupled to the combustion controller and disposed to sense aconcentration of a gas of interest within the flue and convey processinformation related to the concentration to the combustion controller inaccordance with an all-digital process communication protocol; andwherein the in situ flue gas analyzer is communicatively coupled to asecond device and communicates with the second device, in accordancewith a second process communication protocol different than theall-digital process communication protocol, wherein communication withthe combustion controller and the second device occurs substantiallysimultaneously.
 8. The process combustion control system of claim 7,wherein the gas of interest is oxygen.
 9. The process combustion controlsystem of claim 7, wherein the in situ flue gas analyzer communicateswith the combustion controller at a first communication rate, andcommunicates with the second device at a second rate that is less thanthe first rate.
 10. The process combustion control system of claim 7,wherein the second device is a user interface.
 11. The processcombustion control system of claim 10, wherein the second processcommunication protocol is in accordance with the Highway AddressableRemote Transducer (HART) protocol.
 12. A method of operating an in situflue gas analyzer, the method comprising: disposing a probe of the insitu flue gas analyzer within a flue; measuring a concentration of a gason interest using the probe; communicating information regarding themeasured concentration to a combustion controller in accordance with anall-digital process communication protocol; and communicating with asecond device in accordance with a second process communication protocoldifferent than the all-digital process communication protocol.
 13. Themethod of claim 12, wherein the all-digital process communicationprotocol is the FOUNDATION Fieldbus protocol.
 14. The method of claim13, wherein the second process communication protocol is the HighwayAddressable Remote Transducer (HART) protocol.
 15. The method of claim12, wherein communication with the combustion controller and the seconddevice occurs substantially simultaneously.
 16. The method of claim 15,wherein communication with the combustion controller occurs at a firstcommunication rate, and communication with the second device occurs at asecond rate that is less than the first rate.